Test medium and method for detecting phosphorus segregates in metallic material

ABSTRACT

An aqueous solution containing 0.00005 to 0.2 mol/l of copper ion and 0.0001 to 1.0 mol/l of nitrate ion is effective to detect phosphorus segregates in a metallic material, particularly cast steel. Segregated phosphorus can be detected by etching a surface of steel to be tested, attaching test paper onto the steel surface, applying the aqueous solution to the paper, maintaining the paper in contact with the steel surface until stains appear, and removing the paper from the steel surface. A red print is obtained when the solution is pH 6 or higher. A blue print is obtained by following the above steps, and further treating the paper with a color reagent containing molybdate ion, and then with a reducing agent.

This application is a division of application Ser. No. 765,245, filed8/13/85 now U.S. Pat. No. 4,681,857.

BACKGROUND OF THE INVENTION

This invention relates to a test medium and method for detectingphosphorus segregates, and more particularly, to such a method capableof rapidly and easily detecting the distribution of phosphorus inmetallic materials such as continuously cast steel slabs and large-sizedsteel ingots.

Heretofore, segregation in large-sized steel ingots has been judged bysulfur printing. This method is by attaching photographic paperimpregnated with aqueous sulfuric acid to a polished cross section of alarge-sized steel ingot, thereby detecting hydrogen sulfide given offfrom segregated sulfur as stains on the photographic paper. This methodhas been widely used on the production line. Recently, however, steelssubjected to low sulfide treatment and Ca treatment, such as steelsresistant to hydrogen embrittlement cracking, have been put intopractical use, and much progress has been made in the art to manufacturehigh purity steel and to minimize sulfur segregation in continuouscastings. Such advanced steels having extremely low sulfur contents aredifficult to detect solidification segregates by the conventional sulfurprinting. It is thus desirable to detect phosphorus rather than sulfurfor examining segregation.

Aside from the sulfur printing described above, a macroanalyzer is knownas a device for examining the segregation of alloying elements. Themacroanalyzer can quantitatively evaluate a planar section of alarge-sized steel ingot by applying an electron beam to the section anddetecting the spectrum of X-rays generated as in EPMA. However, thismethod is not applicable to a commercial production process because ituses an expensive device, the surface to be examined must be finished byemery paper of the order of #1,000, the measurement of a sample takesmore than one hour, the configuration of a sample is limited, it cannotbe applied to a wide section sample, and so on.

One known method of detecting phosphorus is the phosphorus printingreported by M. Niessner in 1932. This method is by attaching filterpaper which has been immersed in liquid II shown below in Table 1 to asurface of steel to be examined for 3-5 minutes, removing the paper fromthe steel surface, and thereafter dipping the filter paper into liquid Ifor 3-5 minutes, thereby producing a printed image.

                  TABLE 1                                                         ______________________________________                                        Liiquid I                                                                     Stannous chloride saturated solution                                                                  5       ml                                            Concentrated hydrochloric acid                                                                        50      ml                                            Water                   100     ml                                            Alum                    minor amount                                          Liquid II                                                                     Ammonium molybdate      5       g                                             Water                   100     ml                                            Nitric acid (specific gravity 1.2)                                                                    35      ml                                            ______________________________________                                    

Since the specimen surface is maintained in contact with 1.8 N nitricacid, the matrix is severely attacked and phosphorus is dissolved outthere. When the removed test paper is dipped in liquid I, it turns blueover the entire surface. This method is only useful to estimate theamount of phosphorus in the matrix, but difficult to detect phosphorussegregates in commercial grade steels (see FIGS. 12 and 24).

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a novel improvedtest medium and method capable of rapidly detecting and recordingsegregates in metallic materials such as Ca-loaded steels andlow-sulfide steels over a large surface area as easily as by the sulfurprinting described above. In this method, the element to be detected inplace of sulfur is phosphorus, which has the great likelihood tosegregate upon solidifying, and phosphorus segregates are detected ontest paper as stains.

It is therefore, another object of the present invention to provide anovel method for detecting phosphorus segregation which takes the placeof the conventional phosphorus printing method, can produce a clearprinted image with high sensitivity through an easy printing operation,and is suitable for use in the control of an in-place productionprocess.

As will be understood from the following description, the presentprocess is called blue process when segregates are detected as bluespots and called red process when segregates are detected as red spots.

The blue process is first described.

According to a first aspect of the present invention, there is provideda test medium for use in detecting phosphorus segregates in a metallicmaterial, in the form of an aqueous solution containing 0.00005 to 0.2mol/l of copper ion and 0.0001 to 1.0 mol/l of nitrate ion.

According to a second aspect of the present invention, there is provideda test medium for use in detecting phosphorus segregates in a metallicmaterial, in the form of a sheet impregnated with an aqueous solutioncontaining 0.00005 to 0.2 mol/l of copper ion and 0.0001 to 1.0 mol/l ofnitrate ion.

According to a third aspect of the present invention, there is provideda test medium for use in detecting phosphorus segregates in a metallicmaterial, in the form of a sheet having an effective amount of copperand nitrate incorporated therein in a dry state.

According to a fourth aspect of the present invention, there is provideda method for detecting phosphorus segregates in a metallic material,comprising

(a) attaching a test sheet onto that surface of a metallic material tobe tested,

(b) maintaining the sheet in contact with the metallic material surfacein the presence of an aqueous solution comprising 0.00005 to 0.2 mol/lof copper ion and 0.0001 to 1.0 mol/l of nitrate ion for a sufficienttime,

(c) removing the sheet from the metallic material surface, and

(d) treating the sheet from step (c) with a developing or colorproducing agent including molybdate.

According to an fifth aspect, the method as defined above furthercomprises

(e) treating the sheet from step (d) with a reducing agent.

According to a sixth aspect, the method as defined above furthercomprises etching the surface of the metallic surface to be tested priorto step (a).

Next, the red process is descibed.

According to another aspect of the present invention, there is provideda test medium for use in detecting phosphorus segregates in a metallicmaterial, in the form of an aqueous solution containing 0.00005 to 0.2mol/l of copper ion and 0.0001 to 1.0 mol/l of nitrate ion and having apH of at least 6.

According to the present invention, there is also provided a test mediumfor use in detecting phosphorus segregates in a metallic material, inthe form of a sheet impregnated with an aqueous solution containing0.00005 to 2 mol/l of copper ion and 0.0001 to 1.0 mol/l of nitrate ionand having a pH of at least 6.

According to the present invention, there is also provided a test mediumfor use in detecting phosphorus segregates in a metallic material, inthe form of a sheet having an effective amount of copper and nitrateincorporated therein in a dry state.

According to still another aspect of the present invention, there isprovided a method for detecting phosphorus segregates in a metallicmaterial, comprising

(a) attaching a test sheet onto that surface of a metallic material tobe tested,

(b) maintaining the sheet in contact with the metallic material surfacein the presence of an aqueous solution comprising 0.00005 to 0.2 mol/lof copper ion and 0.0001 to 1.0 mol/l of nitrate ion at pH of at least6.0 for a sufficient time, and

(c) removing the sheet from the metallic material surface.

According to a further aspect, the method as defined above furthercomprises etching the surface of the metallic surface to be tested priorto step (a).

The metallic materials to which the present invention is applicable aregenerally carbon steels and low-alloy steels.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood when taken in conjunctionwith the accompanying drawings, in which:

FIGS. 1 to 10 are photographic phosphorus prints representing phosphorussegregates in continuously cast steel billets in Examples 1 to 10;

FIGS. 11, 12 and 13 are photographs taken on the same billet region bysulfur printing, conventional phosphorus printing, and a macroanalyzer,respectively;

FIGS. 14 to 21 are photographic phosphorus prints showing phosphorussegregates in continuously cast billet used in Examples 11 to 14 andExmaples 15 to 18;

FIGS. 22 and 23 are macroanalyzer photographs showing segregatedphosphorus patterns in the same regions as shown in FIGS. 14-17 andFIGS. 18-21, respectively; and

FIGS. 24 and 25 are photographs taken on the same billet region bysulfur printing and conventional phosphorus printing, respectivley.

DETAILED DESCRIPTION OF THE INVENTION

The principle of the present invention will be briefly described. Likesulfur, phosphorus has the great likelihood of segregating uponsolidification and is thus concentrated at the finally solidifiedregion. Phosphorus rich portions are lower in electrochemical series andpreferentially dissolved in etching solution. Ogura et al. reported inJournal of Japanese Metallurgy Associate, 45, 10, 1093 (1981), that thedepth of grooves at grain boundary in steel etched with picric acidetchant is in quantitative relationship to the quantity of phosphorussegregated at grain boundary.

The inventors have found that by virtue of the preferential etching ofphosphorus concentrated portions, phosphorus segregated on a solidifiedsteel slab can be readily detected as blue spots in a short time byintroducing an aqueous solution containing 0.00005 to 0.2 mol/l ofcopper ion and 0.0001 to 1.0 mol/l of nitrate ion, between that surfaceof the steel to be tested and a test sheet on which a pattern ofphosphorus segregation is printable, followed by treating with a colorproducing agent and subsequently with a reducing agent. By introducingan aqueous solution containing 0.0005 to 0.2 mol/l of copper ion and0.0001 to 1.0 mol/l of nitrate ion and having pH adjusted to at least6.0 between that surface of the steel to be tested and a test sheet onwhich a pattern of phosphorus segregation is printable, red coloredspots or stains representing segregated phosphorus appear on the surfaceof the test sheet. In this red process, post-treatments like colorproduction and reduction are unnecessary.

The copper and nitrate ions used herein have the function topreferentially etch or attack electrochemically poorer local phosphorussegregates. Iron ions eluted from the segregated portion are adsorbedonto the test sheet where they precipitate as iron hydroxide, enablingdetection of segregated phosphorus.

The sheets used in the practice of the invention may be any desiredsheet-like articles of materials capable of bearing copper ion andnitrate ion such as wood and synthetic resins, and preferably paper, andmost preferably baryta paper, but not limited thereto.

In any embodiment, it is necessary that an aqueous solution containing0.00005 mol/l to 0.2 mol/l of copper ion and 0.0001 mol/l to 1.0 mol/lof nitrate ion contacts the surface of steel to be tested. Solutionscontaining less than 0.00005 mol/l of copper ion and 0.0001 mol/l ofnitrate ion attack the steel too weakly to detect segregated phosphorusbecause stains or colored spots on a print is blurred whereasconcentrations of higher than 0.2 mol/l of copper ion or 1.0 mol/l ofnitrate ion result in deposits of the salt on the sheet and sticking ofthe sheet onto the specimen surface, rendering the sheet unuseful.

When applied by the red process the aqueous solution containing thespecific amounts of copper and nitrate ions may preferably be adjustedto pH 6.0 or higher to facilitate the precipitation of iron ions elutedfrom the matrix as ferric hydroxide and ferric oxides onto the testsheet. By maintaining the test sheet in pressure contact with thespecimen surface for several minutes, there is obtained a print clearlyshowing spots of segregated phosphorus as stains.

Examples of the cupric ion-supplying compounds include copper chlorideCuCl₂, copper sulfate CuSO₄, copper bromide CuBr₂, copper carboxylateCu(COOH)₂, and copper acetate Cu(CH₃ COO)₂.

Examples of the nitrate ion suppling compounds include ammonium nitrateNH₄ NO₃, sodium nitrate NaNO₃, potassium nitrate KNO₃, lithium nitrateLiNO₃, magnesium nitrate Mg(NO₃)₂ and calcium nitrate Ca(NO₃)₂.

The medium for detecting segregated phosphorus may vary in form.According to a first embodiment of the present invention, the detectingmedium is in the form of an aqueous solution containing 0.00005 to 0.2mol/l of copper ion and 0.0001 to 1.0 mol/l of nitrate ion. The solutionmay usually have a wider range of pH from about 0 to about 10,preferably lower pH, and especially pH of lower than 6 when it is usedby the blue process. It should have a higher pH range from 6 to 14 whenit is used by the red process. On use, a dry sheet or coupon is attachedonto the surface of steel to be tested and the aqueous solution isapplied to the sheet as by spraying, brushing or coating to cause thesolution to reach the steel surface.

According to a second embodiment of the present invention, the detectingmeans is in the form of a wet sheet or coupon, that is, sheet or couponimpregnated or coated with the above-mentioned aqueous solution. The wetsheet, which has contained copper and nitrate ions in a proper amount,is ready for use, that is, it is simply attached or pressed to thesurface of steel to be tested. In some cases, the test sheet may becoated with the solution immediately before it is pressed to the steelsurface.

According to a third embodiment of the present invention, the detectingmeans is in the form of a dry sheet or coupon having copper and nitrateborn thereon in a dry state. This dry sheet is prepared by impregnatinga sheet with an aqueous solution containing copper and nitrate ionsfollowed by drying. The dry sheet is used by attaching it to the surfaceof steel to be tested, and applying a suitable amount of water to thesheet such that an aqueous solution containing proper amounts of copperand nitrate ions and having an appropriate pH is present between thesteel surface and the sheet.

The test sheets are attached to the surface of steel to be tested andmaintained in contact with the steel surface for several minutes, forexample, 3 to 10 minutes. The sheets are then removed from the steelsurface. Iron ions eluted from the phosphorus segregated portion areadsorbed onto the test sheet and/or precipitated thereon as ironhydroxide if the solution has pH adjusted to 6 or higher, while simlarlyeluted phosphorus is also transferred to the sheet. The resulting sheetshave an image of segregated phosphorus printed thereon.

The thus treated sheets may be immersed in a color developing orproducing reagent, such as a reagent containing molybdate ion, andsensitive organic reagents such as macharite green. Examples of themolybdate ion-supplying compounds include ammonium molybdate, sodiummolybdate, lithium molybdate, potassium molybdate, calcium molybdate,and magnesium molybdate.

The eluted phosphorus on the sheet may be developed with color reagentson the basis of molybdenum blue process. A typical example of the colorreagent is an aqueous solution containing 0.1 to 10% by weight ofmolybdate ion and 0.5 to 5 N nitric acid. When the test sheet removedfrom the specimen surface is immersed in the color reagent, molybdenumyellow is formed at the site of eluted phosphorus, thereby enabling thedetection of phosphorus segregates as yellow stains or spots.

When color reagents contain nitric acid of a normality outside theabove-mentioned range or less than 0.1% by weight of ammonium molybdate,the amount of molybdenum yellow produced is insufficient to detect thesegregation, whereas more than 10% by weight of molybdate ion makesdifficult the identification of phosphorus segregates because of thecoloring of molybdate ion itself.

The thus developed sheet may further be treated with a reagentcontaining reducing agents. Examples of the reducing agents includestannous chloride, hydroquinone, hydrazine sulfate, ascorbic acid, etc.A typical reducing reagent is an aqueous solution containing 0.1 to 20%by weight of stannous chloride and 0.5 to 6 N hydrochloric acid.Concentrations of less than 0.1% by weight of stannous chloride are noteffective enough, while concentrations of more than 20% by weightproduce no further reducing effect. Hydrochloric acid of less than 0.5 Ncauses the reduction of molybdate itself, and normalities of more than 6N result in undesirable operating conditions due to vapor emission ofconcentrated hydrochloric acid. Other reducing agents may also be usedin appropreate concentrations such that they have similar reducingeffect as described above.

As understood from the above-mentioned principle of the presentinvention, the surface of steel to be tested for the presence ofsegregated phosphorus may preferably be etched prior to theabove-described detecting process. The etching solutions used for theprevious etching may be solutions containing at least one of mineralacids, organic acids and salts thereof, and an alcohol. Once the surfaceof steel to be tested is attacked by such an etching solution, theetching solution is removed and the steel surface is subjected to theabove-described testing process.

Examples of the acids include mineral acids such as hydrochloric acid,sulfuric acid, perchloric acid, phosphoric acid, nitric acid, etc.;organic acids such as picric acid, salicylic acid, sulfosalicylic acid,acetic acid, formic acid, lactic acid, malic acid, etc.; and salts suchas lithium chloride, copper chloride, calcium chloride, zinc chloride,iron chloride, aluminum chloride, copper sulfate, copper nitrate,tetramethyl ammonium chloride, etc. The alcohols which promote theattack on metal by acid may be any desired alcohols, for example, loweralkyl alcohols such as methanol, ethanol, and propanol as long as theyare liquid at room temperature. The concentrations of acid and alcoholin the etching solution may vary with the characteristics of the steelsurface to be tested including phosphorus concentration and the onlyrequirement is that the alcohol is compatible with the acid in thesolution.

Examples of the present invention are presented below by way ofillustration and not by way of limitation.

The following examples are by the blue process.

EXAMPLE 1

A steel specimen was sectioned from a segregated region of acontinuously cast slab of ordinary carbon steel having a phosphoruscontent of 0.02% by weight. It was polished with #240 emery paper andfully cleaned with absorbent wadding. A wet test paper coupon which wasimpregnated with an aqueous solution of 1% by weight of cupric chlorideand 10% by weight of ammonium nitrate was attached to the surface of thespecimen to be tested and maintained in pressure contact for 5 minutes.The test paper having an image of segregates developed was removed fromthe specimen surface, developed for 10 minutes with an aqueous solutionof 2% by weight of ammonium molybdate and 1.75N nitric acid, reduced for10 minutes with an aqueous solution of 7% by weight of stannous chlorideand 4N hydrochloric acid, and thoroughly washed with water. There wasobtained a printed image as shown in FIG. 1.

EXAMPLE 2

A steel specimen was taken out, polished, and cleaned in the same manneras in Example 1. A test paper coupon free of any agent was attached tothe surface of the specimen to be tested. Absorbent wadding full of anaqueous solution containing 1% by weight of cupric sulfate and 10% byweight of lithium nitrate was forced to and moved throughout the paperto fully wet the paper. The paper was maintained in pressure contactwith the specimen surface for 5 minutes. The test paper was removed fromthe specimen surface, developed for 10 minutes with an aqueous solutionof 2% by weight of ammonium molybdate and 1.75N nitric acid, reduced for10 minutes with an aqueous solution of 7% by weight of stannous chlorideand 4N hydrochloric acid, and thoroughly washed with water. There wasobtained a printed image as shown in FIG. 2.

EXAMPLE 3

A steel specimen was taken out, polished, and cleaned in the same manneras in Example 1. A dry test paper coupon containing 6 grams of cupricnitrate per square meter was attached to the surface of the specimen tobe tested. Absorbent wadding full of water was forced to and movedthroughout the paper such that the test paper was fully wetted with thecopper nitrate solution. The paper was maintained in pressure contactwith the specimen surface for 5 minutes. The test paper was removed fromthe specimen surface, developed for 10 minutes with an aqueous solutionof 2% by weight of ammonium molybdate and 1.75N nitric acid, reduced for10 minutes with an aqueous solution of 7% by weight of stannous chlorideand 4N hydrochloric acid, and thoroughly washed with water. There wasobtained a printed image as shown in FIG. 3.

EXAMPLE 4

A steel specimen was taken out, polished, and cleaned in the same manneras in Example 1. A wet test paper coupon which was impregnated with anaqueous solution of 5% by weight of cupric nitrate was attached to thesurface of the specimen to be tested and maintained in pressure contactfor 5 minutes. The test paper was removed from the specimen surface,developed for 10 minutes with an aqueous solution of 2% by weight ofammonium molybdate and 1.75N nitric acid, and thoroughly washed withwater. The resulting sheet was a print showing segregated phosphorus asyellow spots, as shown in FIG. 4.

EXAMPLE 5

A steel specimen was taken out, polished, and cleaned in the same manneras in Example 1. A test paper coupon free of any agent was attached tothe surface of the specimen to be tested. Absorbent wadding full of anaqueous solution containing 5% by weight of cupric nitrate was forced toand moved throughout the paper to fully wet the paper. The paper wasmaintained in pressure contact with the specimen surface for 5 minutes.The test paper was removed from the specimen surface, developed for 10minutes with an aqueous solution of 2% by weight of ammonium molybdateand 1.75N nitric acid, reduced for 10 minutes with an aqueous solutionof 7% by weight of stannous chloride and 4N hydrochloric acid, andthoroughly washed with water. There was obtained a printed image asshown in FIG. 5.

EXAMPLE 6

A freshly sectioned surface of a segregated region of a continuouslycast slab of ordinary carbon steel having a phosphorus content of 0.02%by weight was polished with #180 emery paper and fully cleaned withabsorbent wadding wetted with ethanol. The specimen was immersed in a 5vol% hydrochloric acid/ethanol solution for 5 minutes for etching. Theetched specimen was fully cleaned with an alcohol and dried. A testsheet impregnated with an aqueous solution containing 7% by weight ofcupric nitrate was attached to the surface of the specimen to be tested.The sheet was maintained in pressure contact with the specimen surfacefor 5 minutes. The test sheet was removed from the specimen surface,developed for 10 minutes with an aqueous solution of 2% by weight ofammonium molybdate and 1.75N nitric acid, reduced for 10 minutes with anaqueous solution of 7% by weight of stannous chloride and 4Nhydrochloric acid, and thoroughly washed with water. There was obtaineda printed image as shown in FIG. 6.

EXAMPLE 7

A freshly sectioned surface of a segregated region of a continuouslycast slab of ordinary carbon steel having a phosphorus content of 0.02%by weight was polished with #180 emery paper and fully cleaned withabsorbent wadding wetted with ethanol. The specimen was immersed in asaturated picric acid/ethanol solution for 5 minutes for etching. Theetched specimen was fully cleaned with ethanol and dried. A test sheetwas attached to the specimen, wetted with an aqueous solution of 7% byweight cupric nitrate, and maintained in pressure contact with thespecimen surface for 5 minutes. The test sheet was removed from thespecimen surface, developed for 10 minutes with an aqueous solution of2% by weight of ammonium molybdate and 1.75N nitric acid, reduced for 10minutes with an aqueous solution of 7% by weight of stannous chlorideand 4N hydrochloric acid, and thoroughly washed with water. There wasobtained a printed image as shown in FIG. 7.

EXAMPLE 8

A freshly sectioned surface of a segregated region of a continuouslycast slab of ordinary carbon steel having a phosphorus content of 0.02%by weight was polished with #180 emery paper and fully cleaned withabsorbent wadding wetted with ethanol. The specimen was immersed in a 5wt % ferric chloride/ethanol solution for 5 minutes for etching. Theetched specimen was fully cleaned with ethanol and dried. A dry testsheet containing 6 grams per square meter of cupric nitrate was attachedto the specimen Absorbent wadding full of water was forced to and movedthroughout the paper such that the test paper was fully wetted with thecopper nitrate solution The sheet was maintained in pressure contactwith the specimen surface for 5 minutes. The test sheet was removed fromthe specimen surface, developed for 10 minutes with an aqueous solutionof 2% by weight of ammonium molybdate and 1.75N nitric acid, reduced for10 minutes with an aqueous solution of 7% by weight of stannous chlorideand 4N hydrochloric acid, and thoroughly washed with water. There wasobtained a printed image as shown in FIG. 8.

EXAMPLE 9

A freshly sectioned surface of a segregated region of a continuouslycast slab of ordinary carbon steel having a phosphorus content of 0.02%by weight was polished with #180 emery paper and fully cleaned withabsorbent wadding wetted with ethanol. The specimen was immersed in amethanol solution of 4% by weight salicylic acid and 2% by weightlithium chloride for 5 minutes for etching. The etched specimen wasfully cleaned with ethanol and dried. A test sheet wetted with anaqueous solution of 1% by weight of cupric nitrate and 10% by weight ofammonium nitrate was attached to the specimen and maintained in pressurecontact with the specimen surface for 5 minutes. The test sheet wasremoved from the specimen surface, developed for 10 minutes with anaqueous solution of 2% by weight of ammonium molybdate and 1.75N nitricacid, reduced for 10 minutes with an aqueous solution of 7% by weight ofstannous chloride and 4N hydrochloric acid, and thoroughly washed withwater. There was obtained a printed image as shown in FIG. 9.

EXAMPLE 10

A freshly sectioned surface of a segregated region of a continuouslycast slab of ordinary carbon steel having a phosphorus content of 0.02%by weight was polished with 180 emery paper and fully cleaned withabsorbent wadding wetted with ethanol. The specimen was immersed in a 5vol% hydrochloric acid/ethanol solution for 5 minutes for etching. Theetched specimen was fully cleaned with alcohol and dried. A test sheetwetted with an aqueous solution containing 7% by weight of cupricnitrate was attached to the surface of specimen to be tested. The testsheet was maintained in pressure contact with the specimen surface for 5minutes. The test sheet was removed from the specimen surface, developedfor 10 minutes with an aqueous solution of 2% by weight of ammoniummolybdate and 1.75N of nitric acid, and thoroughly washed with water.There was obtained a printed image as shown in FIG. 10.

FIGS. 11, 12 and 13 are photographs taken on the same steel slab as usedin Examples 1-10, by means of a sulfur printing, conventional phosphorusprinting and a macroanalyzer, respectively. With respect to thephosphorus distribution pattern on a cross section of cast steel, theprinted images shown in FIGS. 1-10 conform to the macroanalyzerphotographs of FIGS. 13, proving that the present invention is fullyeffective in detecting phosphorus segregation. FIGS. 11 and 12 aredifficult to detect phosphorus segregation. It should be noted that theprints of FIGS. 1-10 correspond of the macroanalyzer photograph of FIG.13 but are mirror images thereof about a vertical center line. Thepresent invention allows the microstructure to be observed as well asthe central segregation.

The following examples are by the red process.

EXAMPLE 11

A steel specimen was sectioned from a segregated region of acontinuously cast slab of ordinary carbon steel having a phosphoruscontent of 0.02% by weight. It was polished with #240 emery paper andfully cleaned with dry absorbent wadding. A wet test paper coupon whichwas impregnated with an aqueous solution adjusted to pH 7.5 andcontaining by weight of cupric nitrate and 10% by weight of ammoniumnitrate and 50% by volume of ethanol was attached to the surface of thespecimen to be tested and maintained in pressure contact for 5 minutesThe test paper was then removed from the specimen surface There wasobtained a printed image as shown in FIG. 14.

EXAMPLE 12

A steel specimen was taken out, polished, and cleaned in the same manneras in Example 11. A wet test paper coupon which was impregnated with anaqueous solution adjusted to pH 7.0 and containing 5% by weight ofcupric nitrate was attached to the surface of the specimen to be testedand maintained in pressure contact for 5 minutes. The test paper wasthen removed from the specimen surface. There was obtained a printedimage as shown in FIG. 15.

EXAMPLE 13

A steel specimen was taken out, polished, and cleaned in the same manneras in Example 11. A test paper coupon free of any agent was attached tothe surface of the specimen to be tested. Absorbent wadding full of anaqueous solution adjusted to pH 7.5 and containing 1% by weight ofcupric chloride and 10% by weight of lithium nitrate was forced to andmoved throughout the paper to fully wet the paper. The paper wasmaintained in pressure contact with the specimen surface for 5 minutesThe test paper was then removed from the specimen surface. There wasobtained a printed image as shown in FIG. 16.

EXAMPLE 14

A steel specimen was taken out, polished, and cleaned in the same manneras in Example 11. A test paper coupon free of any agent was attached tothe surface of the specimen to be tested. Absorbent wadding full of anaqueous solution adjusted to pH 8.0 and containing 5% by weight ofcupric nitrate was forced to and moved throughout the paper to fully wetthe paper The paper was maintained in pressure contact with the specimensurface for 5 minutes. The test paper was then removed from the specimensurface. There was obtained a printed image as shown in FIG. 17.

EXAMPLE 15

A freshly sectioned surface of a segregated region of a continuouslycast slab of ordinary carbon steel having a phosphorus content of 0.02%by weight was polished with #180 emery paper and fully cleaned withabsorbent wadding wetted with ethanol. The specimen was immersed in a 5vol % hydrochloric acid/ethanol solution for 5 minutes for etching. Theetched specimen was fully cleaned with an alcohol and then a test sheetwetted with an aqueous solution adjusted to pH 7.5 containing 7% byweight of copper nitrate was attached to the specimen for 5 minutes. Thetest sheet was then removed from the specimen surface. There wasobtained a printed image as shown in FIG. 18.

EXAMPLE 16

A freshly sectioned surface of a segregated region of a continuouslycast slab of ordinary carbon steel having a phosphorus content of 0.02%by weight was polished with #180 emery paper and fully cleaned withabsorbent wadding wetted with ethanol. The specimen was immersed in asaturated picric acid/ethanol solution for 5 minutes for etching. Theetched specimen was fully cleaned with ethanol. A test sheet was thenattached to the specimen, wetted with an aqueous solution of 7% byweight cupric nitrate at pH 7.0, and maintained in contact with thespecimen surface for 5 minutes. The test sheet was then removed from thespecimen surface. There was obtained a printed image as shown in FIG.19.

EXAMPLE 17

A freshly sectioned surface of a segregated region of a continuouslycast slab of ordinary carbon steel having a phosphorus content of 0.02%by weight was polished with #180 emery paper and fully cleaned withabsorbent wadding wetted with ethanol The specimen was immersed in anethanol solution of 5% by weight ferric chloride for 5 minutes foretching. The etched specimen was fully cleaned with ethanol. A testsheet wetted with an aqueous solution adjusted to pH 8.0 and containing1% by weight cupric chloride and 10% by weight of ammonium nitrate wasattached to the specimen for 5 minutes The test sheet was then removedfrom the specimen surface There was obtained a printed image as shown inFIG. 20.

EXAMPLE 18

A freshly sectioned surface of a segregated region of a continuouslycast slab of ordinary carbon steel having a phosphorus content of 0.02%by weight was polished with #180 emery paper and fully cleaned withabsorbent wadding wetted with ethanol The specimen was immersed in amethanol solution of 4% by weight salicylic acid and 2% by weight oflithium chloride for 5 minutes for etching. The etched specimen wasfully cleaned with ethanol A test sheet was attached to the specimen,wetted with an aqueous solution at pH 7.5 of 1% by weight cupricchloride and 10% by weight ammonium nitrate, and maintained in contactwith the specimen surface for 5 minutes. The test sheet was then removedfrom the specimen surface There was obtained a printed image as shown inFIG. 21.

FIGS. 22 and 23 are macroanalyzer photographs showing segregatedphosphorus patterns in regions corresponding to those shown in FIGS.14-17 and FIGS. 18-21. FIGS. 24 and 25 are photographs taken by sulfurprinting and conventional phosphorus printing, respectively. Withrespect to the phosophrus distribution pattern on a cross section ofcast steel, the printed images shown in FIGS. 14-21 conform to themacroanalyzer photographs of FIGS. 22 and 23, proving that the presentinvention is fully effective in detecting phosphorus segregation. FIGS.24 and 25 are difficult to detect phosphorus segregation. It should benoted that the prints of FIGS. 14-21 are the mirror images of themacroanalyzer photograph of FIGS. 22 and 23.

EFFECT OF THE INVENTION

As seen from the foregoing examples, the present invention allowssegregated phosphorus to be detected without limitation on the size andshape of steel products to be tested. It has been found that thisinvention allows for detection of segregates in low sulfur steels andCa-treated steels which could not be detected by the conventional sulfurprinting Furthermore, unlike the sulfur printing, it eliminatestroublesome operation in a dark room. Since no particular installationis needed for the detecting process because of the elimination ofgeneration of any deleterious gases, the practice of the presentinvention is very easy during continuous steel casting in actual works.The present invention is thus very useful and benefitable in steelmaking It is also very convenient that prints showing segregatedphosphorus can be stored as records.

What we claim is:
 1. A test medium for use in detecting phosphorussegregates in a metallic material, comprising a wet sheet of paperimpregnated with an aqueous solution containing 0.00005 to 0.2 mol/l ofcopper ion and 0.0001 to 1.0 mol/l of nitrate ion.
 2. A test medium foruse in detecting phosphorus segregates in a metallic material,comprising a sheet of paper having an effective amount of cooper ionsupplying compound and nitrate ion supplying compound incorporatedtherein in a dry state, said amount being effective to preferentiallyetch a metallic material so as to detect phosphorus segregates when thesheet is saturated with water and applied to a surface of a metallicmaterial.
 3. A test medium for use in detecting phosphorus segregates ina metallic material, comprising a wet sheet of paper impregnated with anaqueous solution containing 0.00005 to 0.2 mol/l of copper ion and0.0001 to 1.0 mol/l of nitrate ion and having a pH of at least
 6. 4. Atest medium for use in detecting phosphorus segregates in a metallicmaterial, comprising a sheet of paper having an effective amount ofcopper ion supplying compound and nitrate ion supplying compoundincorporated therein in a dry state such that there will be formed anaqueous solution containing 0.00005 to 0.2 mol/l of copper ion and0.0001 to 1.0 mol/l of nitrate ion and having a pH of at least 6 whenthe sheet is saturated with water, said amount being effective topreferentially etch a metallic material so as to detect phosphorussegregates when the sheet saturated with water is applied to a surfaceof a metallic material.